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Mesophyll Protoplasts (mesophyll + protoplast)

Distribution by Scientific Domains
Life Sciences100%

Selected Abstracts

Importance of AOX pathway in optimizing photosynthesis under high light stress: role of pyruvate and malate in activating AOX

PHYSIOLOGIA PLANTARUM, Issue 1 2010
Challabathula Dinakar
The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O2 evolution and O2 uptake in mesophyll protoplasts of pea pre-incubated under different light intensities. Under HL (3000 µmol m,2 s,1), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO3 -dependent O2 evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O2 uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO3 -dependent O2 evolution or p -benzoquinone (BQ)-dependent O2 evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model. [source]

Functional dissection of the cytosolic chaperone network in tomato mesophyll protoplasts

PLANT CELL & ENVIRONMENT, Issue 2 2009
JOANNA TRIPP
ABSTRACT The heat stress response is universal to all organisms. Upon elevated temperatures, heat stress transcription factors (Hsfs) are activated to up-regulate the expression of molecular chaperones to protect cells against heat damages. In higher plants, the phenomenon is unusually complex both at the level of Hsfs and heat stress proteins (Hsps). Over-expression of both Hsfs and Hsps and the use of RNA interference for gene knock-down in a transient system in tomato protoplasts allowed us to dissect the in vivo chaperone functions of essential components of thermotolerance, such as the cytoplasmic sHsp, Hsp70 and Hsp100 chaperone families, and the regulation of their expression. The results point to specific functions of the different components in protection from protein denaturation and in refolding of denatured proteins. [source]

AtKC1, a conditionally targeted Shaker-type subunit, regulates the activity of plant K+ channels

THE PLANT JOURNAL, Issue 1 2008
Geoffrey Duby
Summary Amongst the nine voltage-gated K+ channel (Kv) subunits expressed in Arabidopsis, AtKC1 does not seem to form functional Kv channels on its own, and is therefore said to be silent. It has been proposed to be a regulatory subunit, and to significantly influence the functional properties of heteromeric channels in which it participates, along with other Kv channel subunits. The mechanisms underlying these properties of AtKC1 remain unknown. Here, the transient (co-)expression of AtKC1, AKT1 and/or KAT1 genes was obtained in tobacco mesophyll protoplasts, which lack endogenous inward Kv channel activity. Our experimental conditions allowed both localization of expressed polypeptides (GFP-tagging) and recording of heterologously expressed Kv channel activity (untagged polypeptides). It is shown that AtKC1 remains in the endoplasmic reticulum unless it is co-expressed with AKT1. In these conditions heteromeric AtKC1-AKT1 channels are obtained, and display functional properties different from those of homomeric AKT1 channels in the same context. In particular, the activation threshold voltage of the former channels is more negative than that of the latter ones. Also, it is proposed that AtKC1-AKT1 heterodimers are preferred to AKT1-AKT1 homodimers during the process of tetramer assembly. Similar results are obtained upon co-expression of AtKC1 with KAT1. The whole set of data provides evidence that AtKC1 is a conditionally-targeted Kv subunit, which probably downregulates the physiological activity of other Kv channel subunits in Arabidopsis. [source]

Negative regulation of defense responses in Arabidopsis by two NPR1 paralogs

THE PLANT JOURNAL, Issue 5 2006
Yuelin Zhang
Summary NPR1 is required for systemic acquired resistance, and there are five NPR1 paralogs in Arabidopsis. Here we report knockout analysis of two of these, NPR3 and NPR4. npr3 single mutants have elevated basal PR-1 expression and the npr3 npr4 double mutant shows even higher expression. The double mutant plants also display enhanced resistance against virulent bacterial and oomycete pathogens. This enhanced disease resistance is partially dependent on NPR1, can be in part complemented by either wild-type NPR3 or NPR4, and is not associated with an elevated level of salicylic acid. NPR3 and NPR4 interact with TGA2, TGA3, TGA5 and TGA6 in yeast two-hybrid assays. Using bimolecular fluorescence complementation analysis, we show that NPR3 interacts with TGA2 in the nucleus of onion epidermal cells and Arabidopsis mesophyll protoplasts. Combined with our previous finding that basal PR-1 levels are also elevated in the tga2 tga5 tga6 triple mutant, we propose that NPR3 and NPR4 negatively regulate PR gene expression and pathogen resistance through their association with TGA2 and its paralogs. [source]